In general, such a monoblock injection pump and nozzle uses a common housing for accommodating a piston pump as well as an injection nozzle. The piston pump includes a cylinder liner and a piston running within the cylinder liner. The piston controls one or more flow passages which radially extend in the cylinder liner and communicate with a supply space defined between the housing and the piston pump. Within this supply space, a baffle sleeve is arranged in vicinity of the flow passage to provide two chambers which communicate with each other.
The baffle sleeves used in such fuel injection units avoid an erosion of the housing wall along the area facing the flow passage because the returning sharp fuel jet discharged through the flow passage is deflected by the baffle sleeve and thus is prevented from inpinging upon the housing walls. The baffle sleeves are thus, however, subjected to wear and must be replaceable after a certain period even when made of special low wear materials.
From the German specifications DE-OS No. 24 42 010 and DE-OS No. 24 42 088 as well as from the German Pat. No. 11 72 897, fuel injection units are known which employ such baffle sleeves to subdivide the supply space. Leading into the supply space is one fuel line which provides the supply as well as the discharge of fuel. Consequently, only a slight circulation without any preferred direction prevails in the supply space. This leads to an accumulation of air bubbles.
The presence of air bubbles is disadvantageous as the pump delivery is irregular and eventually causes injection of a fluctuating fuel quantity resulting in an irregular engine output. Moreover, since the fuel is heated up in each injection unit of a corresponding cylnder to a different level, the low circulation is insufficient to provide a balancing to compensate for these different temperatures.
The German Pat. No. 958 440 describes the use of separate inlet and outlet lines for the fuel; however, this patent is concerned with a different construction, i.e. the inlet and outlet are not in communication with a common fuel supply space.